听力原文: Let's begin today by discussing enzymes. Enzymes are what make many of the body's biochemical reactions possible. Actually biochemical reactions can take place without them, but at much lower rates. In fact an enzyme may cause a reaction to proceed billions of times faster than it would otherwise. Before I go on to the biochemical specifics of how this works, let me provide a figurative example. I think it will help illustrate the power of enzymes more clearly. Now, suppose you got a bag and you put a bunch of locks in it, just small padlocks. Then you put in all the keys that go with the locks. And you closed the bag and shook it hard. No matter how long you shook, chances are very small that any key would get inserted in any of the locks. But if you took them all out of the bag and this time used your hands to insert the keys in the locks, you could combine them much quicker.
Enzymes act like your hands, quickly allowing chemical reactions that would otherwise take much longer. Now, there are 2 reasons that enzymes are so effective at enabling biochemical reactions. Firs enzymes greatly reduce the amount of energy required to start the reactions, and with less energy needed the reactions can proceed a lot faster than they, could without the enzyme. The second mason is that on a small amount of an enzyme is needed to enable the biochemical reaction. That's because the chemical structure of the enzyme itself does not become altered as if enables the reaction. So a single enzyme can be used to start the same biochemical reaction over and over again.
(43)
A.The impact of enzymes on chemical reactions.
B.The way the body produces enzymes.
C.The structure of enzymes.
D.Types of chemical products created with enzymes.
第1题
下列关于眼睛和眼镜的说法中不正确的是()
A.人的眼睛相当于凸透镜
B.近视眼的折光能力太强
C.近视眼看远处的物体不清晰
D.近视眼镜镜片就是凸透镜
第3题
A.明视距离小于25cm的是近视眼,应戴凸透镜
B.明视距离大于25cm的是远视眼,应戴凸透镜
C.明视距离大于25cm的是近视眼,应戴凹透镜
D.明视距离小于25cm的是远视眼,应戴凹透镜
第4题
A.远视眼,用凸透镜矫正
B.远视眼,用凹透镜矫正
C.近视眼,用凸透镜矫正
D.近视眼,用凹透镜矫正
第5题
A.近视眼成像于视网膜后,用凸透镜矫正
B.远视眼成像于视网膜后,用凹透镜矫正
C.近视眼成像于视网膜前,用凹透镜矫正
D.远视眼成像于视网膜前,用凸透镜矫正
第7题
A.攻击手段从纯技术手段转为技术+人+网上+网下
B.攻击目标从打哪指哪转为指哪打哪
C.攻击来源从集团作战转向单打独斗
D.攻击线路从定向入侵转到旁路入侵
第8题
A.真性近视和假性近视均表现为远点视力下降
B.假性近视是因为过度使用调节使眼的屈光力增强而形成的近视状态
C.假性近视需尽早配戴眼镜矫正
D.假性近视是器质性改变
E.真性近视是功能性改变
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